1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device which is capable of reducing the brightness irregularities (Mura) which appear on a display screen while enhancing the brightness of the display screen.
2. Description of the Related Art
A liquid crystal display device has been widely used as a display device for personal computers, monitors, television sets and the like.
This liquid crystal display device includes a liquid crystal display panel which is comprised of a pair of substrates, a liquid crystal layer sandwiched between a pair of these substrates (a layer formed of liquid crystal composition sealed between a pair of substrates) and a group of electrodes which are formed on a main surface of at least one of a pair of substrates which faces the liquid crystal layer in an opposed manner.
In a display operation of the liquid crystal display device, an electric field applied to the inside of the liquid crystal layer by the above-mentioned group of electrodes is controlled in response to information to be displayed so as to modulate the light transmissivity of the liquid crystal layer.
Here, in the main surface of the above-mentioned substrate of the liquid crystal display panel, a region where the light transmissivity of the above-mentioned liquid crystal layer is modulated (region where the above-mentioned display operation is performed) is referred to as “effective display region”.
The liquid crystal display device is roughly classified into two types, that is, an active matrix type and a passive matrix type depending on the behavior of liquid crystal molecules in the inside of the above-mentioned liquid crystal layer in the display operation and the electrode structure in the inside of the above-mentioned liquid crystal display panel which is adapted to the behavior.
The former liquid crystal display device is characterized by forming active elements in respective pixels which constitute the above-mentioned effective display region and, particularly, a product which uses thin film transistors (referred to as “TFT” (Thin Film Transistor)) as the active elements has been popularly used.
The liquid crystal display panel which uses the thin film transistors is referred to as a TFT-type liquid crystal display panel or a TFT panel.
Further, as a liquid crystal display panel which belongs to the passive matrix type, an STN (Super Twisted Nematic) type liquid crystal display has been widely used, for example.
In general, a liquid crystal display device is used in a state that the device is incorporated in a personal computer, a monitor, a television set or the like. Accordingly, the liquid crystal display device is provided as a “liquid crystal display module” in assembling steps of the personal computer, the monitor or the television set.
The liquid crystal display module is constituted of a liquid crystal display panel which arranges driver circuit parts around the panel and a backlight unit which irradiates light to the liquid crystal display panel.
For example, a TFT-type liquid crystal display module is formed such that a filter substrate on which color filters are formed and a TFT substrate on which pixel electrodes and thin film transistors (TFT) are formed are superposed to have surfaces thereof on which orientation films are formed to face each other in an opposed manner by means of sealing material formed on peripheral portions of both substrates, and liquid crystal is filled and sealed between both substrates thus forming the liquid crystal display panel.
Such a technique is described in Japanese Patent Laid-Open No. 19474/1985 and Japanese Patent Laid-Open No. 22780/1992, for example.